1. Field of the Invention
The present invention relates to a unit intended to form one or more layers from individual flat supports or substrates. The invention also relates to a machine for producing packaging comprising such a unit for forming this or these layers.
2. Description of the Related Art
In a machine for producing packaging, an initial flat printing substrate, such as a continuous strip of cardboard, is successively unwound, printed and cut to a given shape. Each of the cutouts or boxes obtained is intended to form an item of packaging once it has been folded and glued. To make the packaging easier to assemble, the cutouts often have flaps extending from each of their sides and scoring to make the sides of the packaging easier to fold.
Once these cutouts have been produced, the initial substrate is then conveyed through a separation unit so as to position the various cutouts in several adjacent parallel lines. The separation unit causes the cutouts to deviate slightly from the initial longitudinal direction. It is possible afterwards to realign each of the cutouts in the same main direction using one or more alignment modules located downstream of the separator. This alignment module generally takes the form of two conveyor belts facing one another and one above the other. Each of the cutouts is inserted and moved at high speed between the two belts. The alignment modules, and therefore the cutouts, are distant from one another.
The next step is then to route each of these cutouts to the stacking station. However, the cutouts can be stacked and bundled correctly only if the cutouts are moving slowly. It is necessary to reduce the speed of the cutouts as they leave the alignment module. This slowing is generally achieved by transferring the cutouts onto a conveyor device situated downstream of the alignment module, the conveyor device moving at a lower speed by comparison with that of the conveyor device formed by the alignment module.
In order to reduce the length of the stacking and bundling unit and thus of the machine, it proves necessary to create a layer of cutouts. Thus, as many lines of layers are formed as there are cutouts across the width of the initial substrate. The cutouts are laid on one another with overlap as the flow of cutouts progresses. This arrangement and this progression of the cutouts in layer form also make it possible to maintain a constant rate of production.
The layer is formed by a transfer and by a speed differential between a first conveyor device, that conveys the cutouts quickly, and a second conveyor device that conveys the layer more slowly (see, for example, documents U.S. Pat. No. 3,942,786 and FR 2 784 085). The first conveyor device is either the alignment module or ramps of the separation unit.
Problems with recurrent jams have been noted in this transfer region. These jams are often caused by the difficulty in setting down a cutout that is moving at high speed and relatively freely on to a layer of cutouts that has already been formed and is moving more slowly. The speed differential between the rapidly-moving cutout and the slow-moving layer may notably result in incorrect orientation of the cutout once it has been set down on the layer. If this is not detected and corrected in time, this incorrect orientation may then in turn impede the setting-down of the next cutouts.
In many cases, one cutout becomes caught or even wedged in another, notably at their flaps, tabs, rim edges, cutouts, embossing or any other modifications. This wedging therefore causes jams which force the operator regularly to shut down the unit so that the normal flow of cutouts can be re-established.
This difficulty in correctly positioning the cutouts leaving the first conveyor device is also exacerbated by the way in which the cutouts behave while they are being transferred to the slow-moving second conveyor device. The second conveyor device is generally situated lower down than the exit from the first conveyor device, i.e. the alignment module. The cutouts are released from this exit before they reach the slow-moving conveyor device. As they fall, they are therefore subjected to the air currents generated by the conveyor devices or by the cutouts themselves. Their small thickness and relative lightness of weight therefore cause them to oscillate about an ideal path. It is therefore often difficult to control the path followed by the cutouts while they are being transferred at the instant that they arrive in the unit that forms them into a layer.
One first system for controlling the path of the cutouts is to insert a plurality of deflectors between the exit from the first conveyor device and the entrance to the second conveyor device. However, even though these deflectors appreciably reduce the risk of jams at relatively slow speeds, they prove to be insufficient when the cutouts are moving very quickly. In that case, the air currents generated within the machine have far too disturbing an influence on the path of the cutouts for the deflectors really to be able to confer an ideal path on the cutouts. Moreover, even at slow speeds, it is often necessary regularly and individually to readjust each of the deflectors in order to guarantee uniformity in the flow of the cutouts.
To supplement these deflectors, use is also made of press rollers positioned transversely to the slow-moving conveyor device in order to press firmly on the top of the lines of layers of cutouts. These press rollers are generally positioned just after the deflectors so as to press the cutouts leaving the first conveyor device firmly against the layer that is in the process of forming. These rollers therefore contribute to decelerating the cutouts from a high speed to a slow speed. However, these rollers prove to be incapable of limiting the risk of the cutouts becoming wedged in one another, notably at their respective flaps.
In the devices of the related art, the position of a substrate in the layer fluctuates further in the first few moments following its introduction to the layer because its speed has not yet become stabilized. It therefore has a tendency to slip on the substrate preceding it. This slippage further increases the risk of these substrates becoming wedged together and, therefore, of causing a jam in the unit.